Documenting a Unesco WH Site in Cyprus with Complementary Techniques

Abstract

According to UNESCO directives, the documentation of monuments is a complex task, which both terrestrial laser scanning (TLS) and photogrammetry can decisively support. Today, these techniques are considered complementary, as they demonstrate clear advantages and disadvantages to each other, with regard to representation, texture application, data gathering, acquisition and processing time, practicality, accuracy, data density, surface reflectivity and absorption. In an effort to clarify which part should be acquired with which technique, as well as to understand whether one technique has a clear advantage over the other in some specific task of the documentation process, the Church of the Holy Cross in Pelendri, Cyprus, which is a UNESCO World Heritage monument, was selected as a test site. The deliverables are orthophotos, sections, plots and a complete and accurate 3D model of the monument. The whole documentation process has been carried out independently using an image based technique with Menci's ZScan and terrestrial laser scanning Leica's ScanStation 2, supported by high resolution digital images. Data acquisition has been carried out in parallel while the final products have been created independently by each one. It is clear that the processing phase of photogrammetry is more time consuming than the equivalent in TLS, but high quality texturing and the orthophoto production process are included within the processing, hence image based techniques present an advantage. As for their final accuracy, both techniques deliver satisfactory results within the required scale tolerances. Their individual merits are also presented, discussed and evaluated in this paper.